Yamaha audio inputs
Here is something I noticed on my lower end Yamaha HTR-5860 that might help for your application. I had a CD player hooked up to the analog CD input and the TV's digital audio output (for OTA antenna) hooked up the the digital optical input which was assigned to CD. When the TV was off, I got the analog CD input, however, if both were on, it would output audio from the digital input. This might work if you have a SD cable box with analog outputs.